// Copyright 2009 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

// HTTP file system request handler

package fileserver

import (
    "net/http"
    "errors"
    "fmt"
    "io"
    "mime"
    "mime/multipart"
    "net/textproto"
    "net/url"
    "os"
    "path"
    "path/filepath"
    "strconv"
    "strings"
    "time"
)

// A Dir implements FileSystem using the native file system restricted to a
// specific directory tree.
//
// While the FileSystem.Open method takes '/'-separated paths, a Dir's string
// value is a filename on the native file system, not a URL, so it is separated
// by filepath.Separator, which isn't necessarily '/'.
//
// An empty Dir is treated as ".".
type Dir string

func (d Dir) Open(name string) (http.File, error) {
    if filepath.Separator != '/' && strings.IndexRune(name, filepath.Separator) >= 0 ||
    strings.Contains(name, "\x00") {
        return nil, errors.New("http: invalid character in file path")
    }
    dir := string(d)
    if dir == "" {
        dir = "."
    }
    f, err := os.Open(filepath.Join(dir, filepath.FromSlash(path.Clean("/"+name))))
    if err != nil {
        return nil, err
    }
    return f, nil
}

// A FileSystem implements access to a collection of named files.
// The elements in a file path are separated by slash ('/', U+002F)
// characters, regardless of host operating system convention.
type FileSystem interface {
    Open(name string) (http.File, error)
}

// A File is returned by a FileSystem's Open method and can be
// served by the FileServer implementation.
//
// The methods should behave the same as those on an *os.File.

//type File interface {
//    io.Closer
//    io.Reader
//    Readdir(count int) ([]os.FileInfo, error)
//    Seek(offset int64, whence int) (int64, error)
//    Stat() (os.FileInfo, error)
//}

type File http.File

func dirList(w http.ResponseWriter, f File) {
    w.Header().Set("Content-Type", "text/html; charset=utf-8")
    fmt.Fprintf(w, "<pre>\n")
    for {
        dirs, err := f.Readdir(100)
        if err != nil || len(dirs) == 0 {
            break
        }
        for _, d := range dirs {
            name := d.Name()
            if d.IsDir() {
                name += "/"
            }
            // name may contain '?' or '#', which must be escaped to remain
            // part of the URL path, and not indicate the start of a query
            // string or fragment.
            url := url.URL{Path: name}
            fmt.Fprintf(w, "<a href=\"%s\">%s</a>\n", url.String(), htmlReplacer.Replace(name))
        }
    }
    fmt.Fprintf(w, "</pre>\n")
}

var htmlReplacer = strings.NewReplacer(
"&", "&amp;",
"<", "&lt;",
">", "&gt;",
// "&#34;" is shorter than "&quot;".
`"`, "&#34;",
// "&#39;" is shorter than "&apos;" and apos was not in HTML until HTML5.
"'", "&#39;",
)


// ServeContent replies to the request using the content in the
// provided ReadSeeker.  The main benefit of ServeContent over io.Copy
// is that it handles Range requests properly, sets the MIME type, and
// handles If-Modified-Since requests.
//
// If the response's Content-Type header is not set, ServeContent
// first tries to deduce the type from name's file extension and,
// if that fails, falls back to reading the first block of the content
// and passing it to DetectContentType.
// The name is otherwise unused; in particular it can be empty and is
// never sent in the response.
//
// If modtime is not the zero time, ServeContent includes it in a
// Last-Modified header in the response.  If the request includes an
// If-Modified-Since header, ServeContent uses modtime to decide
// whether the content needs to be sent at all.
//
// The content's Seek method must work: ServeContent uses
// a seek to the end of the content to determine its size.
//
// If the caller has set w's ETag header, ServeContent uses it to
// handle requests using If-Range and If-None-Match.
//
// Note that *os.File implements the io.ReadSeeker interface.
func ServeContent(w http.ResponseWriter, req *http.Request, name string, modtime time.Time, content io.ReadSeeker) {

    sizeFunc := func() (int64, error) {
        size, err := content.Seek(0, os.SEEK_END)
        if err != nil {
            return 0, errSeeker
        }
        _, err = content.Seek(0, os.SEEK_SET)
        if err != nil {
            return 0, errSeeker
        }
        return size, nil
    }
    go serveContent(w, req, name, modtime, sizeFunc, content)
}

// errSeeker is returned by ServeContent's sizeFunc when the content
// doesn't seek properly. The underlying Seeker's error text isn't
// included in the sizeFunc reply so it's not sent over HTTP to end
// users.
var errSeeker = errors.New("seeker can't seek")

// if name is empty, filename is unknown. (used for mime type, before sniffing)
// if modtime.IsZero(), modtime is unknown.
// content must be seeked to the beginning of the file.
// The sizeFunc is called at most once. Its error, if any, is sent in the HTTP response.
func serveContent(w http.ResponseWriter, r *http.Request, name string, modtime time.Time, sizeFunc func() (int64, error), content io.ReadSeeker) {
    if checkLastModified(w, r, modtime) {
        return
    }
    rangeReq, done := checkETag(w, r, modtime)
    if done {
        return
    }

    code := http.StatusOK

    // If Content-Type isn't set, use the file's extension to find it, but
    // if the Content-Type is unset explicitly, do not sniff the type.
    ctypes, haveType := w.Header()["Content-Type"]
    var ctype string
    if !haveType {
        ctype = mime.TypeByExtension(filepath.Ext(name))
        if ctype == "" {
            // read a chunk to decide between utf-8 text and binary
            var buf [512]byte
            n, _ := io.ReadFull(content, buf[:])
            ctype = http.DetectContentType(buf[:n])
            _, err := content.Seek(0, os.SEEK_SET) // rewind to output whole file
            if err != nil {
                http.Error(w, "seeker can't seek", http.StatusInternalServerError)
                return
            }
        }
        w.Header().Set("Content-Type", ctype)
    } else if len(ctypes) > 0 {
        ctype = ctypes[0]
    }

    size, err := sizeFunc()
    if err != nil {
        http.Error(w, err.Error(), http.StatusInternalServerError)
        return
    }

    // handle Content-Range header.
    sendSize := size
    var sendContent io.Reader = content
    if size >= 0 {
        ranges, err := parseRange(rangeReq, size)
        if err != nil {
            http.Error(w, err.Error(), http.StatusRequestedRangeNotSatisfiable)
            return
        }
        if sumRangesSize(ranges) > size {
            // The total number of bytes in all the ranges
            // is larger than the size of the file by
            // itself, so this is probably an attack, or a
            // dumb client.  Ignore the range request.
            ranges = nil
        }
        switch {
            case len(ranges) == 1:
            // RFC 2616, Section 14.16:
            // "When an HTTP message includes the content of a single
            // range (for example, a response to a request for a
            // single range, or to a request for a set of ranges
            // that overlap without any holes), this content is
            // transmitted with a Content-Range header, and a
            // Content-Length header showing the number of bytes
            // actually transferred.
            // ...
            // A response to a request for a single range MUST NOT
            // be sent using the multipart/byteranges media type."
            ra := ranges[0]
            if _, err := content.Seek(ra.start, os.SEEK_SET); err != nil {
                http.Error(w, err.Error(), http.StatusRequestedRangeNotSatisfiable)
                return
            }
            sendSize = ra.length
            code = http.StatusPartialContent
            w.Header().Set("Content-Range", ra.contentRange(size))
            case len(ranges) > 1:
            sendSize = rangesMIMESize(ranges, ctype, size)
            code = http.StatusPartialContent

            pr, pw := io.Pipe()
            mw := multipart.NewWriter(pw)
            w.Header().Set("Content-Type", "multipart/byteranges; boundary="+mw.Boundary())
            sendContent = pr
            defer pr.Close() // cause writing goroutine to fail and exit if CopyN doesn't finish.
            go func() {
                for _, ra := range ranges {
                    part, err := mw.CreatePart(ra.mimeHeader(ctype, size))
                    if err != nil {
                        pw.CloseWithError(err)
                        return
                    }
                    if _, err := content.Seek(ra.start, os.SEEK_SET); err != nil {
                        pw.CloseWithError(err)
                        return
                    }
                    if _, err := io.CopyN(part, content, ra.length); err != nil {
                        pw.CloseWithError(err)
                        return
                    }
                }
                mw.Close()
                pw.Close()
            }()
        }

        w.Header().Set("Accept-Ranges", "bytes")
        if w.Header().Get("Content-Encoding") == "" {
            w.Header().Set("Content-Length", strconv.FormatInt(sendSize, 10))
        }
    }

    w.WriteHeader(code)

    if r.Method != "HEAD" {
        io.CopyN(w, sendContent, sendSize)
    }
}

// modtime is the modification time of the resource to be served, or IsZero().
// return value is whether this request is now complete.
func checkLastModified(w http.ResponseWriter, r *http.Request, modtime time.Time) bool {
    if modtime.IsZero() {
        return false
    }

    // The Date-Modified header truncates sub-second precision, so
    // use mtime < t+1s instead of mtime <= t to check for unmodified.
    if t, err := time.Parse(http.TimeFormat, r.Header.Get("If-Modified-Since")); err == nil && modtime.Before(t.Add(1*time.Second)) {
        h := w.Header()
        delete(h, "Content-Type")
        delete(h, "Content-Length")
        w.WriteHeader(http.StatusNotModified)
        //        w.WriteHeader(http.StatusNotModified)
        return true

    }
    w.Header().Set("Last-Modified", modtime.UTC().Format(http.TimeFormat))
    return false
}

//type Header map[string][]string

//func (h mHeader) get(key string) string {
//    if v := h[key]; len(v) > 0 {
//        return v[0]
//    }
//    return ""
//}

func fileGet(h http.Header, key string) string {
    if v := h[key]; len(v) > 0 {
        return v[0]
    }
    return ""
}

// checkETag implements If-None-Match and If-Range checks.
//
// The ETag or modtime must have been previously set in the
// ResponseWriter's headers.  The modtime is only compared at second
// granularity and may be the zero value to mean unknown.
//
// The return value is the effective request "Range" header to use and
// whether this request is now considered done.
func checkETag(w http.ResponseWriter, r *http.Request, modtime time.Time) (rangeReq string, done bool) {
    //    etag := w.Header().get("Etag")
    //   rangeReq = r.Header.get("Range")
    etag := fileGet(w.Header(), "Etag")
    rangeReq = fileGet(w.Header(), "Range")

    // Invalidate the range request if the entity doesn't match the one
    // the client was expecting.
    // "If-Range: version" means "ignore the Range: header unless version matches the
    // current file."
    // We only support ETag versions.
    // The caller must have set the ETag on the response already.
    //    if ir := r.Header.get("If-Range"); ir != "" && ir != etag {
    if ir := fileGet(r.Header, "If-Range"); ir != "" && ir != etag {
        // The If-Range value is typically the ETag value, but it may also be
        // the modtime date. See golang.org/issue/8367.
        timeMatches := false
        if !modtime.IsZero() {
            if t, err := http.ParseTime(ir); err == nil && t.Unix() == modtime.Unix() {
                timeMatches = true
            }
        }
        if !timeMatches {
            rangeReq = ""
        }
    }

    //    if inm := r.Header.get("If-None-Match"); inm != "" {
    if inm := fileGet(r.Header, "If-None-Match"); inm != "" {
        // Must know ETag.
        if etag == "" {
            return rangeReq, false
        }

        // TODO(bradfitz): non-GET/HEAD requests require more work:
        // sending a different status code on matches, and
        // also can't use weak cache validators (those with a "W/
        // prefix).  But most users of ServeContent will be using
        // it on GET or HEAD, so only support those for now.
        if r.Method != "GET" && r.Method != "HEAD" {
            return rangeReq, false
        }

        // TODO(bradfitz): deal with comma-separated or multiple-valued
        // list of If-None-match values.  For now just handle the common
        // case of a single item.
        if inm == etag || inm == "*" {
            h := w.Header()
            delete(h, "Content-Type")
            delete(h, "Content-Length")
            w.WriteHeader(http.StatusNotModified)
            return "", true
        }
    }
    return rangeReq, false
}

// name is '/'-separated, not filepath.Separator.
func serveFile(w http.ResponseWriter, r *http.Request, fs FileSystem, name string, redirect bool) {
    const indexPage = "/index.html"

    // redirect .../index.html to .../
    // can't use Redirect() because that would make the path absolute,
    // which would be a problem running under StripPrefix
    if strings.HasSuffix(r.URL.Path, indexPage) {
        localRedirect(w, r, "./")
        return
    }

    f, err := fs.Open(name)
    if err != nil {
        // TODO expose actual error?
        http.NotFound(w, r)
        return
    }
    defer f.Close()

    d, err1 := f.Stat()
    if err1 != nil {
        // TODO expose actual error?
        http.NotFound(w, r)
        return
    }

    if redirect {
        // redirect to canonical path: / at end of directory url
        // r.URL.Path always begins with /
        url := r.URL.Path
        if d.IsDir() {
            if url[len(url)-1] != '/' {
                localRedirect(w, r, path.Base(url)+"/")
                return
            }
        } else {
            if url[len(url)-1] == '/' {
                localRedirect(w, r, "../"+path.Base(url))
                return
            }
        }
    }

    // use contents of index.html for directory, if present
    if d.IsDir() {
        index := strings.TrimSuffix(name, "/") + indexPage
        ff, err := fs.Open(index)
        if err == nil {
            defer ff.Close()
            dd, err := ff.Stat()
            if err == nil {
                name = index
                d = dd
                f = ff
            }
        }
    }

    // Still a directory? (we didn't find an index.html file)
    if d.IsDir() {
        if checkLastModified(w, r, d.ModTime()) {
            return
        }
        dirList(w, f)
        return
    }

    // serveContent will check modification time
    sizeFunc := func() (int64, error) { return d.Size(), nil }
    serveContent(w, r, d.Name(), d.ModTime(), sizeFunc, f)
}

// localRedirect gives a Moved Permanently response.
// It does not convert relative paths to absolute paths like Redirect does.
func localRedirect(w http.ResponseWriter, r *http.Request, newPath string) {
    if q := r.URL.RawQuery; q != "" {
        newPath += "?" + q
    }
    w.Header().Set("Location", newPath)
    w.WriteHeader(http.StatusMovedPermanently)
}

// ServeFile replies to the request with the contents of the named file or directory.
func ServeFile(w http.ResponseWriter, r *http.Request, name string) {
    dir, file := filepath.Split(name)
    serveFile(w, r, Dir(dir), file, false)
}

type fileHandler struct {
    root FileSystem
}

// FileServer returns a handler that serves HTTP requests
// with the contents of the file system rooted at root.
//
// To use the operating system's file system implementation,
// use http.Dir:
//
//     http.Handle("/", http.FileServer(http.Dir("/tmp")))
func FileServer(root FileSystem) http.Handler {
    return &fileHandler{root}
}

func (f *fileHandler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
    //    w.Write([]byte("Go is running"))
    fmt.Println(r.RemoteAddr)

    upath := r.URL.Path
    if !strings.HasPrefix(upath, "/") {
        upath = "/" + upath
        r.URL.Path = upath
    }
    serveFile(w, r, f.root, path.Clean(upath), true)
    //   w.WriteHeader(http.StatusOK)
}

// httpRange specifies the byte range to be sent to the client.
type httpRange struct {
    start, length int64
}

func (r httpRange) contentRange(size int64) string {
    return fmt.Sprintf("bytes %d-%d/%d", r.start, r.start+r.length-1, size)
}

func (r httpRange) mimeHeader(contentType string, size int64) textproto.MIMEHeader {
    return textproto.MIMEHeader{
        "Content-Range": {r.contentRange(size)},
        "Content-Type":  {contentType},
    }
}

// parseRange parses a Range header string as per RFC 2616.
func parseRange(s string, size int64) ([]httpRange, error) {
    if s == "" {
        return nil, nil // header not present
    }
    const b = "bytes="
    if !strings.HasPrefix(s, b) {
        return nil, errors.New("invalid range")
    }
    var ranges []httpRange
    for _, ra := range strings.Split(s[len(b):], ",") {
        ra = strings.TrimSpace(ra)
        if ra == "" {
            continue
        }
        i := strings.Index(ra, "-")
        if i < 0 {
            return nil, errors.New("invalid range")
        }
        start, end := strings.TrimSpace(ra[:i]), strings.TrimSpace(ra[i+1:])
        var r httpRange
        if start == "" {
            // If no start is specified, end specifies the
            // range start relative to the end of the file.
            i, err := strconv.ParseInt(end, 10, 64)
            if err != nil {
                return nil, errors.New("invalid range")
            }
            if i > size {
                i = size
            }
            r.start = size - i
            r.length = size - r.start
        } else {
            i, err := strconv.ParseInt(start, 10, 64)
            if err != nil || i > size || i < 0 {
                return nil, errors.New("invalid range")
            }
            r.start = i
            if end == "" {
                // If no end is specified, range extends to end of the file.
                r.length = size - r.start
            } else {
                i, err := strconv.ParseInt(end, 10, 64)
                if err != nil || r.start > i {
                    return nil, errors.New("invalid range")
                }
                if i >= size {
                    i = size - 1
                }
                r.length = i - r.start + 1
            }
        }
        ranges = append(ranges, r)
    }
    return ranges, nil
}

// countingWriter counts how many bytes have been written to it.
type countingWriter int64

func (w *countingWriter) Write(p []byte) (n int, err error) {
    *w += countingWriter(len(p))
    return len(p), nil
}

// rangesMIMESize returns the number of bytes it takes to encode the
// provided ranges as a multipart response.
func rangesMIMESize(ranges []httpRange, contentType string, contentSize int64) (encSize int64) {
    var w countingWriter
    mw := multipart.NewWriter(&w)
    for _, ra := range ranges {
        mw.CreatePart(ra.mimeHeader(contentType, contentSize))
        encSize += ra.length
    }
    mw.Close()
    encSize += int64(w)
    return
}

func sumRangesSize(ranges []httpRange) (size int64) {
    for _, ra := range ranges {
        size += ra.length
    }
    return
}

